1. Field of the Invention
The present invention relates to a driving circuit for an image display apparatus, an image display apparatus using this circuit, and a driving method for them.
2. Description of the Related Art
In recent years, low-profile, large-screen display apparatuses have enthusiastically been studied and developed. The present inventor has studied a low-profile, large-screen display apparatus using a cold cathode device as an electron source.
Two types of devices, namely hot and cold cathode devices, are conventionally known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction emission type electron-emitting devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
A known example of the surface-conduction emission type electron-emitting devices is described in, e.g., M. I. Elinson, “Radio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction emission type electron-emitting device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction emission type electron-emitting device includes electron-emitting devices using an Au thin film [G. Dittmer, “Thin Solid Films”, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, “IEEE Trans. ED Conf.”, 519 (1975)], a carbon thin film [Hisashi Araki et al., “Vacuum”, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 19 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction emission type electron-emitting devices. Referring to FIG. 19, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 19. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 19 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm. The electron-emitting portion 3005 is shown in a rectangular shape at the center of the conductive thin film 3004 for the sake of illustrative convenience. However, this does not exactly show the actual position and shape of the electron-emitting portion.
In the above surface-conduction emission type electron-emitting devices by M. Hartwell et al. and the like, typically the electron-emitting portion 3005 is formed by performing electrification processing called forming processing for the conductive thin film 3004 before electron emission. In the forming processing, an electron-emitting portion is formed by electrification such that a constant DC voltage or a DC voltage which increases at a very low rate of, e.g., 1 V/min is applied across the two ends of the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the destroyed or deformed part of the conductive thin film 3004 has a fissure. Upon application of an appropriate voltage to the conductive thin film 3004 after the forming processing, electrons are emitted near the fissure.
These surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, “Field emission,” Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, “Physical properties of thin-film field emission cathodes with molybdenium cones,” J. Appl. Phys., 47, 5248 (1976).
FIG. 20 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. In FIG. 20, reference numeral 3010 denotes a substrate; 3011, an emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, agate electrode. In this device, an appropriate voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012. As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 20.
A known example of the MIM type electron-emitting devices is described in C.A. Mead, “Operation of Tunnel-Emission Devices”, J. Appl. Phys., 32,646 (1961). FIG. 21 shows a typical example of the MIM type device structure. FIG. 21 is a sectional view of the MIM type electron-emitting device. In FIG. 21, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 Å; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 Å. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the cold cathode device can emit electrons at a lower temperature than a hot cathode device, it does not require any heater. The cold cathode is simpler in structure than the hot cathode device and can shrink in feature size. Even if a large number of devices can be arranged at a high density, they are almost free from problems such as heat fusion of the substrate. In addition, the response speed of the hot cathode device is low because it operates upon heating. To the contrary, the response speed of the cold cathode device is high. For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the above surface-conduction emission type electron-emitting devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction emission type electron-emitting devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, charge beam sources, and the like have been studied.
Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,833 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using the combination of a surface-conduction emission type electron-emitting device and a fluorescent substance which emits light upon irradiation of an electron beam has been studied. This type of image display apparatus using the combination of the surface-conduction emission type electron-emitting device and the fluorescent substance is expected to exhibit more excellent characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is of a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An example of an application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
The present inventors have examined surface-conduction emission type electron-emitting devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned conventional surface-conduction emission type electron-emitting devices. Further, the present inventors have made extensive studies on a multi electron source having a large number of surface-conduction emission type electron-emitting devices, and an image display apparatus using this multi electron source. The present inventors have examined a multi electron source having an electrical wiring method shown in, e.g., FIG. 22. That is, a large number of surface-conduction emission type electron-emitting devices are two-dimensionally arranged in a matrix to obtain a multi electron source, as shown in FIG. 22.
Referring to FIG. 22, reference numeral 4001 denotes a surface-conduction emission type electron-emitting device; 4002, a row-direction wiring; and 4003, a column-direction wiring. The row- and column-direction wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 22. This wiring method is called a simple matrix wiring method. For illustrative convenience, the multi electron source is illustrated in a 6×6 matrix, but the size of the matrix is not limited to this. For example, in a multi beam source for an image display apparatus, the number of devices enough to perform desired image display are arranged and wired.
In a multi electron source constituted by arranging surface-conduction emission type electron-emitting devices in a simple matrix, appropriate electrical signals are applied to the row- and column-direction wirings 4002 and 4003 to output a desired electron beam. For example, to drive the surface-conduction emission type electron-emitting devices on an arbitrary row in the matrix, a selection potential Vs is applied to the row-direction wiring 4002 on a selected row, and at the same time a non-selection potential Vns is applied to the row-direction wirings 4002 on an unselected row. In synchronism with this, a driving potential Ve for outputting an electron beam is applied to the column-direction wiring 4003. According to this method, when voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Ve-Vs) is applied to the surface-conduction emission type electron-emitting devices on the selected row, while a voltage (Ve-Vns) is applied to the surface-conduction emission type electron-emitting devices on the unselected row. When the potentials Ve, Vs, and Vns are set to appropriate magnitudes, an electron beam having a desired intensity must be output from only the surface-conduction emission type electron-emitting devices on the selected row. When different driving voltages Ve are applied to respective column-direction wirings, electron beams having different intensities must be output from the respective devices on the selected row. Since the surface-conduction emission type electron-emitting device has a high response speed, a change in length of time for which the driving voltage Ve is applied necessarily causes a change in length of time for which an electron beam is output.
The device application voltage (Ve−Vs) in selection will be called Vf.
As another method of obtaining an electron beam from a multi electron source having a simple matrix wiring, column-direction wirings are connected to not a voltage source for applying the driving potential Ve but a current source for applying a driving current. The selection potential Vs is applied to a row-direction wiring on a selected row, and at the same time the non-selection potential Vns is applied to a row-direction wiring on an unselected row. Then, an electron beam can be obtained from only the devices on the selected row owing to a strong threshold characteristic of the surface-conduction emission type electron-emitting device. The current flowing through the electron source will be called a device current If, and an emitted electron beam current will be called an emission current Ie.
The multi electron source constituted by arranging surface-conduction emission type electron-emitting devices in a simple matrix has a variety of applications. For example, when an electrical signal corresponding to image information is appropriately applied, the multi electron source can be suitably used as an electron source for an image display apparatus.
An object of the present invention is to realize an arrangement capable of more accurately displaying an image.